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blocked_evals.go
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blocked_evals.go
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package nomad
import (
"sync"
"time"
"github.com/armon/go-metrics"
"github.com/hashicorp/consul/lib"
"github.com/hashicorp/nomad/nomad/structs"
)
const (
// unblockBuffer is the buffer size for the unblock channel. The buffer
// should be large to ensure that the FSM doesn't block when calling Unblock
// as this would apply back-pressure on Raft.
unblockBuffer = 8096
)
// BlockedEvals is used to track evaluations that shouldn't be queued until a
// certain class of nodes becomes available. An evaluation is put into the
// blocked state when it is run through the scheduler and produced failed
// allocations. It is unblocked when the capacity of a node that could run the
// failed allocation becomes available.
type BlockedEvals struct {
evalBroker *EvalBroker
enabled bool
stats *BlockedStats
l sync.RWMutex
// captured is the set of evaluations that are captured by computed node
// classes.
captured map[string]wrappedEval
// escaped is the set of evaluations that have escaped computed node
// classes.
escaped map[string]wrappedEval
// unblockCh is used to buffer unblocking of evaluations.
capacityChangeCh chan *capacityUpdate
// jobs is the map of blocked job and is used to ensure that only one
// blocked eval exists for each job. The value is the blocked evaluation ID.
jobs map[string]string
// unblockIndexes maps computed node classes to the index in which they were
// unblocked. This is used to check if an evaluation could have been
// unblocked between the time they were in the scheduler and the time they
// are being blocked.
unblockIndexes map[string]uint64
// duplicates is the set of evaluations for jobs that had pre-existing
// blocked evaluations. These should be marked as cancelled since only one
// blocked eval is neeeded per job.
duplicates []*structs.Evaluation
// duplicateCh is used to signal that a duplicate eval was added to the
// duplicate set. It can be used to unblock waiting callers looking for
// duplicates.
duplicateCh chan struct{}
// stopCh is used to stop any created goroutines.
stopCh chan struct{}
}
// capacityUpdate stores unblock data.
type capacityUpdate struct {
computedClass string
index uint64
}
// wrappedEval captures both the evaluation and the optional token
type wrappedEval struct {
eval *structs.Evaluation
token string
}
// BlockedStats returns all the stats about the blocked eval tracker.
type BlockedStats struct {
// TotalEscaped is the total number of blocked evaluations that have escaped
// computed node classes.
TotalEscaped int
// TotalBlocked is the total number of blocked evaluations.
TotalBlocked int
}
// NewBlockedEvals creates a new blocked eval tracker that will enqueue
// unblocked evals into the passed broker.
func NewBlockedEvals(evalBroker *EvalBroker) *BlockedEvals {
return &BlockedEvals{
evalBroker: evalBroker,
captured: make(map[string]wrappedEval),
escaped: make(map[string]wrappedEval),
jobs: make(map[string]string),
unblockIndexes: make(map[string]uint64),
capacityChangeCh: make(chan *capacityUpdate, unblockBuffer),
duplicateCh: make(chan struct{}, 1),
stopCh: make(chan struct{}),
stats: new(BlockedStats),
}
}
// Enabled is used to check if the broker is enabled.
func (b *BlockedEvals) Enabled() bool {
b.l.RLock()
defer b.l.RUnlock()
return b.enabled
}
// SetEnabled is used to control if the blocked eval tracker is enabled. The
// tracker should only be enabled on the active leader.
func (b *BlockedEvals) SetEnabled(enabled bool) {
b.l.Lock()
if b.enabled == enabled {
// No-op
b.l.Unlock()
return
} else if enabled {
go b.watchCapacity()
} else {
close(b.stopCh)
}
b.enabled = enabled
b.l.Unlock()
if !enabled {
b.Flush()
}
}
// Block tracks the passed evaluation and enqueues it into the eval broker when
// a suitable node calls unblock.
func (b *BlockedEvals) Block(eval *structs.Evaluation) {
b.processBlock(eval, "")
}
// Reblock tracks the passed evaluation and enqueues it into the eval broker when
// a suitable node calls unblock. Reblock should be used over Block when the
// blocking is occurring by an outstanding evaluation. The token is the
// evaluation's token.
func (b *BlockedEvals) Reblock(eval *structs.Evaluation, token string) {
b.processBlock(eval, token)
}
// processBlock is the implementation of blocking an evaluation. It supports
// taking an optional evaluation token to use when reblocking an evaluation that
// may be outstanding.
func (b *BlockedEvals) processBlock(eval *structs.Evaluation, token string) {
b.l.Lock()
defer b.l.Unlock()
// Do nothing if not enabled
if !b.enabled {
return
}
// Check if the job already has a blocked evaluation. If it does add it to
// the list of duplicates. We omly ever want one blocked evaluation per job,
// otherwise we would create unnecessary work for the scheduler as multiple
// evals for the same job would be run, all producing the same outcome.
if _, existing := b.jobs[eval.JobID]; existing {
b.duplicates = append(b.duplicates, eval)
// Unblock any waiter.
select {
case b.duplicateCh <- struct{}{}:
default:
}
return
}
// Check if the eval missed an unblock while it was in the scheduler at an
// older index. The scheduler could have been invoked with a snapshot of
// state that was prior to additional capacity being added or allocations
// becoming terminal.
if b.missedUnblock(eval) {
// Just re-enqueue the eval immediately. We pass the token so that the
// eval_broker can properly handle the case in which the evaluation is
// still outstanding.
b.evalBroker.EnqueueAll(map[*structs.Evaluation]string{eval: token})
return
}
// Mark the job as tracked.
b.stats.TotalBlocked++
b.jobs[eval.JobID] = eval.ID
// Wrap the evaluation, capturing its token.
wrapped := wrappedEval{
eval: eval,
token: token,
}
// If the eval has escaped, meaning computed node classes could not capture
// the constraints of the job, we store the eval separately as we have to
// unblock it whenever node capacity changes. This is because we don't know
// what node class is feasible for the jobs constraints.
if eval.EscapedComputedClass {
b.escaped[eval.ID] = wrapped
b.stats.TotalEscaped++
return
}
// Add the eval to the set of blocked evals whose jobs constraints are
// captured by computed node class.
b.captured[eval.ID] = wrapped
}
// missedUnblock returns whether an evaluation missed an unblock while it was in
// the scheduler. Since the scheduler can operate at an index in the past, the
// evaluation may have been processed missing data that would allow it to
// complete. This method returns if that is the case and should be called with
// the lock held.
func (b *BlockedEvals) missedUnblock(eval *structs.Evaluation) bool {
var max uint64 = 0
for class, index := range b.unblockIndexes {
// Calculate the max unblock index
if max < index {
max = index
}
elig, ok := eval.ClassEligibility[class]
if !ok && eval.SnapshotIndex < index {
// The evaluation was processed and did not encounter this class
// because it was added after it was processed. Thus for correctness
// we need to unblock it.
return true
}
// The evaluation could use the computed node class and the eval was
// processed before the last unblock.
if elig && eval.SnapshotIndex < index {
return true
}
}
// If the evaluation has escaped, and the map contains an index older than
// the evaluations, it should be unblocked.
if eval.EscapedComputedClass && eval.SnapshotIndex < max {
return true
}
// The evaluation is ahead of all recent unblocks.
return false
}
// Untrack causes any blocked evaluation for the passed job to be no longer
// tracked. Untrack is called when there is a successful evaluation for the job
// and a blocked evaluation is no longer needed.
func (b *BlockedEvals) Untrack(jobID string) {
b.l.Lock()
defer b.l.Unlock()
// Do nothing if not enabled
if !b.enabled {
return
}
// Get the evaluation ID to cancel
evalID, ok := b.jobs[jobID]
if !ok {
// No blocked evaluation so exit
return
}
// Attempt to delete the evaluation
if w, ok := b.captured[evalID]; ok {
delete(b.jobs, w.eval.JobID)
delete(b.captured, evalID)
b.stats.TotalBlocked--
}
if w, ok := b.escaped[evalID]; ok {
delete(b.jobs, w.eval.JobID)
delete(b.escaped, evalID)
b.stats.TotalEscaped--
b.stats.TotalBlocked--
}
}
// Unblock causes any evaluation that could potentially make progress on a
// capacity change on the passed computed node class to be enqueued into the
// eval broker.
func (b *BlockedEvals) Unblock(computedClass string, index uint64) {
b.l.Lock()
// Do nothing if not enabled
if !b.enabled {
b.l.Unlock()
return
}
// Store the index in which the unblock happened. We use this on subsequent
// block calls in case the evaluation was in the scheduler when a trigger
// occurred.
b.unblockIndexes[computedClass] = index
b.l.Unlock()
b.capacityChangeCh <- &capacityUpdate{
computedClass: computedClass,
index: index,
}
}
// watchCapacity is a long lived function that watches for capacity changes in
// nodes and unblocks the correct set of evals.
func (b *BlockedEvals) watchCapacity() {
for {
select {
case <-b.stopCh:
return
case update := <-b.capacityChangeCh:
b.unblock(update.computedClass, update.index)
}
}
}
// unblock unblocks all blocked evals that could run on the passed computed node
// class.
func (b *BlockedEvals) unblock(computedClass string, index uint64) {
b.l.Lock()
defer b.l.Unlock()
// Protect against the case of a flush.
if !b.enabled {
return
}
// Every eval that has escaped computed node class has to be unblocked
// because any node could potentially be feasible.
numEscaped := len(b.escaped)
unblocked := make(map[*structs.Evaluation]string, lib.MaxInt(numEscaped, 4))
if numEscaped != 0 {
for id, wrapped := range b.escaped {
unblocked[wrapped.eval] = wrapped.token
delete(b.escaped, id)
delete(b.jobs, wrapped.eval.JobID)
}
}
// We unblock any eval that is explicitly eligible for the computed class
// and also any eval that is not eligible or uneligible. This signifies that
// when the evaluation was originally run through the scheduler, that it
// never saw a node with the given computed class and thus needs to be
// unblocked for correctness.
for id, wrapped := range b.captured {
if elig, ok := wrapped.eval.ClassEligibility[computedClass]; ok && !elig {
// Can skip because the eval has explicitly marked the node class
// as ineligible.
continue
}
// The computed node class has never been seen by the eval so we unblock
// it.
unblocked[wrapped.eval] = wrapped.token
delete(b.jobs, wrapped.eval.JobID)
delete(b.captured, id)
}
if l := len(unblocked); l != 0 {
// Update the counters
b.stats.TotalEscaped = 0
b.stats.TotalBlocked -= l
// Enqueue all the unblocked evals into the broker.
b.evalBroker.EnqueueAll(unblocked)
}
}
// UnblockFailed unblocks all blocked evaluation that were due to scheduler
// failure.
func (b *BlockedEvals) UnblockFailed() {
b.l.Lock()
defer b.l.Unlock()
// Do nothing if not enabled
if !b.enabled {
return
}
unblocked := make(map[*structs.Evaluation]string, 4)
for id, wrapped := range b.captured {
if wrapped.eval.TriggeredBy == structs.EvalTriggerMaxPlans {
unblocked[wrapped.eval] = wrapped.token
delete(b.captured, id)
delete(b.jobs, wrapped.eval.JobID)
}
}
for id, wrapped := range b.escaped {
if wrapped.eval.TriggeredBy == structs.EvalTriggerMaxPlans {
unblocked[wrapped.eval] = wrapped.token
delete(b.escaped, id)
delete(b.jobs, wrapped.eval.JobID)
b.stats.TotalEscaped -= 1
}
}
if l := len(unblocked); l > 0 {
b.stats.TotalBlocked -= l
b.evalBroker.EnqueueAll(unblocked)
}
}
// GetDuplicates returns all the duplicate evaluations and blocks until the
// passed timeout.
func (b *BlockedEvals) GetDuplicates(timeout time.Duration) []*structs.Evaluation {
var timeoutTimer *time.Timer
var timeoutCh <-chan time.Time
SCAN:
b.l.Lock()
if len(b.duplicates) != 0 {
dups := b.duplicates
b.duplicates = nil
b.l.Unlock()
return dups
}
b.l.Unlock()
// Create the timer
if timeoutTimer == nil && timeout != 0 {
timeoutTimer = time.NewTimer(timeout)
timeoutCh = timeoutTimer.C
defer timeoutTimer.Stop()
}
select {
case <-b.stopCh:
return nil
case <-timeoutCh:
return nil
case <-b.duplicateCh:
goto SCAN
}
}
// Flush is used to clear the state of blocked evaluations.
func (b *BlockedEvals) Flush() {
b.l.Lock()
defer b.l.Unlock()
// Reset the blocked eval tracker.
b.stats.TotalEscaped = 0
b.stats.TotalBlocked = 0
b.captured = make(map[string]wrappedEval)
b.escaped = make(map[string]wrappedEval)
b.jobs = make(map[string]string)
b.duplicates = nil
b.capacityChangeCh = make(chan *capacityUpdate, unblockBuffer)
b.stopCh = make(chan struct{})
b.duplicateCh = make(chan struct{}, 1)
}
// Stats is used to query the state of the blocked eval tracker.
func (b *BlockedEvals) Stats() *BlockedStats {
// Allocate a new stats struct
stats := new(BlockedStats)
b.l.RLock()
defer b.l.RUnlock()
// Copy all the stats
stats.TotalEscaped = b.stats.TotalEscaped
stats.TotalBlocked = b.stats.TotalBlocked
return stats
}
// EmitStats is used to export metrics about the blocked eval tracker while enabled
func (b *BlockedEvals) EmitStats(period time.Duration, stopCh chan struct{}) {
for {
select {
case <-time.After(period):
stats := b.Stats()
metrics.SetGauge([]string{"nomad", "blocked_evals", "total_blocked"}, float32(stats.TotalBlocked))
metrics.SetGauge([]string{"nomad", "blocked_evals", "total_escaped"}, float32(stats.TotalEscaped))
case <-stopCh:
return
}
}
}